1. Field of the Invention
The present invention relates to a method for improving the recovery of mineral values from ore bodies subjected to in-situ leaching by controlling the flow behavior of the leaching solution. More particularly, the present invention relates to an in-situ leaching operation employing a foam for mobility control of the leaching solution.
2. Description of the Art
The in situ leaching of mineral values from subterranean deposits is well-known in the art as a practical and economical means for recovering certain elements such as uranium, copper, nickel, molybdenum, rhenium, vanadium and the like. Basically, solution mining is carried out by injecting into the subterranean deposit, a leaching solution which will solubilize the mineral value desired to be recovered and the solution and solubilized mineral values are recovered from the deposit for subsequent separation of the mineral values. Often it is necessary to oxidize the mineral vale to a form where it can form a soluble reaction product in the leaching solution. Depending upon the nature of the subterranean deposit, the typical leaching solution may be an acid, for example, an aqueous sulfuric acid solution or may comprise an alkaline carbonate solution.
The above method, and modifications thereof, works most efficiently when a fairly uniform formation is the subject of the leaching process. All too often, however, and in fact in a majority of cases, the formations are not uniform as to both porosity and permeability. In some zones, the strata are sufficiently heterogeneous as to severely alter flow patterns. Leaching fluids follow the higher permeability streaks thus by-passing portions of the ore body which results in loss of recoverable mineral values due to the lack of contact by leaching fluids.
Foams have been used in petroleum recovery as indicated by U.S. Pat. No. 3,599,715 to Roszelle and U.S. Pat. No. 3,893,511 to Root which show two processes where foam is used for petroleum recovery. In the oil recovery process, the foaming agent, which is normally a surfactant, is of similar material present in the surfactant flooding process. When oil contacts with a foaming agent, then either some oil dissolves in the foaming agent or the oil solubilizes some of the foaming agent. In either case foaming agent loss is realized. In the mineral values leaching process of the present invention, the foam is used solely as a blocking agent without any chemical loss to the leaching solution or residual mineral values. Another difference is that in the oil recovery process, the foaming agent is usually introduced into the formation with another surfactant. The compatability of the two components is not at question. In the mineral values leaching process the foaming agent is introduced with a leaching solution which is of a substantially different chemical composition than the surfactant slug used in oil recovery processes.
It is an object of the present invention to provide an improved in-situ leaching process for formations having substantially non-uniform permeabilities.